Mirror device with an anti-stiction layer

ABSTRACT

A micromirror device includes an elastic hinge for supporting a mirror on a substrate, and an address electrode for deflecting the mirror. The device further includes a protective layer and an oriented monolayer laid to cover a stopper also functioning as an address electrode provided below the mirror and between the mirror and the substrate.

This application is a Non-provisional Application claiming a Prioritydate of May 3, 2007 based on a previously filed Provisional Application60/927,486 filed by the common Applicants of this application and thedisclosures made in Provisional Application 60/927,486 are furtherincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and device configuration of amicromirror device manufactured by applying the technologies of MicroElectro Mechanical Systems (MEMS). More particularly, this inventionrelates to a method and device configuration for manufacturing adeflective micromirror device for preventing stiction between amicromirror and a substrate after an etching process.

2. Description of the Related Arts

After the dominance of CRT technology in the display industry, FlatPanel Display (hereafter FPD) and Projection Display gained popularitybecause of a smaller form-factor and a larger size of screen. In severaltypes of projection displays, projection displays using micro-displaysare gaining consumers' recognition because of high performance of imagequality as well as lower cost than FPDs. There are two types ofmicro-displays used for projection displays in the market. One is amicro-LCD (Liquid Crystal Display) and the other is a display usingmicromirror technology such as a micromirror device. Because themicromirror device uses an un-polarized light, a micromirror device hasan advantage of projecting images with greater brightness than theimages displayed by the micro-LCD devices using the polarized light.

There are semiconductor-processing technologies that include techniquesand systems for generating a micro electro mechanical structure andelectric control circuits supported on a semiconductor substrate toconfigure the above-mentioned micromirror device. These technologies aregenerally referred to as MEMS (micro electro mechanical systems).Recently, the MEMS technologies have been applied in various fields suchas an RF radio oscillator, an acceleration sensor, opticalcommunications, a display, etc. In the display field, the MEMStechnologies have been applied to manufacture a micromirror device ascommercial products in which several millions of substantially squaremirrors of about 10 μm square are arranged vertically and horizontallyin a two-dimensional array.

Even though there are significant advances made on the technologies ofimplementing electromechanical micromirror devices as spatial lightmodulator in recent years, there are still limitations and difficultieswhen it was employed to a high quality image display. Specifically, whenthe display are digitally controlled, the image quality are adverselyaffected due to the fact that the image is not displayed with asufficient number of gray scales.

Electromechanical micromirror devices have drawn considerable interestbecause of their application as spatial light modulators (SLMs). Aspatial light modulator requires an array of a relatively large numberof micromirror elements. In general, the number of micromirror elementsrequired ranges from 60,000 to a several of millions in a SLM.

Referring to FIG. 1A for an image display system 1 including a screen 2is disclosed in a reference U.S. Pat. No. 5,214,420. A light source 10is used for generating light energy for illuminating the screen 2. Thegenerated light 9 is further collimated and directed toward a lens 12 bya mirror 11. Lenses 12, 13 and 14 form a beam columnator operative tocolumnate light 9 into a column of light 8.

A spatial light modulator (SLM) 15 is controlled on the basis of datainput by a computer 19 via a bus 18 and selectively redirects theportions of light from a path 7 toward an enlarger lens 5 and ontoscreen 2. The SLM 15 has a mirror array includes switchable reflectiveelements 17, 27, 37, and 47 each comprising a mirror 33 connected by ahinge 30 and supported on a surface 16 of a substrate in theelectromechanical mirror device as shown in FIG. 1B.

When the element 17 is in one position, a portion of the light from thepath 7 is redirected along a path 6 to lens 5 where it is enlarged orspread along the path 4 to impinge on the screen 2 so as to form anilluminated pixel 3. When the element 17 is in another position, thelight is redirected away from the display screen 2 and hence the pixel 3is dark.

Each of the mirror elements 17, 27, 37, and 47 implemented in amicromirror device 16 as shown in FIGS. 1A and 1B is configured toinclude a micromirror and an address electrode. By applying a voltage tothe address electrode, the micromirror is controlled to tilt by aCoulomb force works between the micromirror and the address electrode.In this specification, the operation that causes “a micromirror tilts”is described as “a micromirror deflects”.

As the Coulomb force deflects the micromirror that also changes thedirection of the reflection of incident light by the deflection angle ofthe mirror. In this specification, the direction of the reflected lightfor projecting almost all incident light toward the light path of imagedisplay is referred to as “ON light”. Conversely, as the reflected lightis projected in the direction away from the light path for imagedisplay, the micromirror is referred to as operation in an “OFF state”.

A micromirror is controlled to operate in an intermediate state duringthe time when the micromirror is deflected in the angular positions whenthe incident light is reflected between the ON-state and the OFF-state.According to the system configuration of this invention, a portion ofthe reflected light smaller the amount of light reflected in theON-state is controlled and directed to project a reduced light intensityfor image display. The levels of gray scales are increased because theleast amount of controllable light projection for image display isreduced.

By applying a voltage to the address electrode, a Coulomb force isgenerated to deflect the surface of the micromirror to different tiltangles and comes into contact with an address electrode or a stoppersupported on the substrate. The tilt angles of the mirror surface ofeach of the mirror elements 17, 27, 37, and 47 are controlled to directto different predefined angles thus allows a control circuit to controlthe reflection of the incident light to the ON light state or the OFFlight state.

Most of the conventional image display devices such as the devicesdisclosed in U.S. Pat. No. 5,214,420 are implemented with a dual-statemirror control that controls the mirrors to operate at a state of eitherON or OFF. The quality of an image display is limited due to the limitednumber of gray scales. Specifically, in a conventional control circuitthat applies a PWM (Pulse Width Modulation), the quality of the image islimited by the LSB (least significant bit) or the least pulse width ascontrol related to the ON or OFF state. Since the mirror is controlledto operate in an either ON or OFF state, the conventional image displayapparatuses have no way to provide a pulse width to control the mirrorthat is shorter than the control duration allowable according to theLSB. The least quantity of light, which determines the least amount ofadjustable brightness for adjusting the gray scale, is the lightreflected during the time duration according to the least pulse width.The limited gray scale due to the LSB limitation leads to a degradationof the quality of the display image.

Specifically, FIG. 1C exemplifies a control circuit for controlling amirror element according to the disclosure in the U.S. Pat. No.5,285,407. The control circuit includes a memory cell 32. Varioustransistors are referred to as “M*” where “*” designates a transistornumber and each transistor is an insulated gate field effect transistor.Transistors M5 and M7 are p-channel transistors; while transistors M6,M8, and M9 are n-channel transistors.

The capacitances C1 and C2 represent the capacitive loads in the memorycell 32. The memory cell 32 includes an access switch transistor M9 anda latch 32 a, which is based on a Static Random Access switch Memory(SRAM) design. The transistor M9 connected to a Row-line receives a DATAsignal via a Bit-line. The memory cell 32-written data is accessed whenthe transistor M9 that has received the ROW signal on a Word-line isturned on. The latch 32 a consists of two cross-coupled inverters, i.e.,M5/M6 and M7/M8, which permit two stable states, that is, a state 1 isNode A high and Node B low, and a state 2 is Node A low and Node B high.

FIG. 1D shows the “binary time periods” in the case of controlling SLMby four-bit words. As shown in FIG. 1D, the time periods have relativevalues of 1, 2, 4, and 8 that in turn determine the relative quantity oflight of each of the four bits, where the “1” is least significant bit(LSB) and the “8” is the most significant bit. According to the PWMcontrol mechanism, the minimum quantity of light that determines theresolution of the gray scale is a brightness controlled by using the“least significant bit” for holding the mirror at an ON position duringa shortest controllable length of time.

In a simple example with n bits word for controlling the gray scale, oneframe time is divided into (2^(n)−1) time slices and each slice has anequal length of time. If one frame time is 16.7 msec., each time sliceis 16.7/(2^(n)−1) msec.

Having fixed the length for each of these time slices for each pixel ofeach frame, the light intensities for displaying each pixel arequantized. A pixel for displaying a black light is assigned with a 0time slice, the intensity level represented by the LSB is 1 time slice,and maximum brightness is 2″−1 time slices. The on-time during a frameperiod controls the pixel's quantized intensity Of display. Thus, duringa frame period, the light intensity of each pixel is controlled tocorrespond with a quantized value of the number of time slices. Theviewer's eye integrates the pixel brightness to perceive the image witha level of brightness as if the images were generated with analog levelsof light.

The pulse width modulator controls the operations of addressing thedeformable mirror devices by formatting the data into “bit-planes” witheach bit-plane corresponding to a bit weight of the intensity value.Therefore, if each pixel's intensity is represented by an n-bit value,each frame of data has n bit-planes. Each bit-plane has a 0 or 1 valuefor each display element. In the PWM control process each bit plane isseparately loaded during a frame and the display elements are addressedaccording to their associated bit-plane values. For example, thebit-plane representing the LSBs of each pixel is displayed for 1 timeslice.

FIG. 2 shows the light 24 is projected from the light source into themicromirror device 16. The micromirror device 16 shown in FIG. 2includes a plurality of mirror elements 23, and the mirror elements 23are arranged as a two-dimensional array. Each mirror element 23 iscontrollable to change the tilt of the mirror surface of a micromirror21 based on a deflection axis 22 by applying a voltage to an addresselectrode. Thus, in the ON light state, the micromirror 21 is controlledto tilt to the deflection angle for reflecting the incident light alongthe direction for projecting images onto the screen.

On the other hand, in the OFF state, the micromirror 21 is controlled totilt to the deflection angle for reflecting the incident lightprojecting along the optical path toward a light dump.

In a practical implementation, the size of each micromirror 21 shown inFIG. 2 is 11 μm. However, taking into account of current trends oftechnological developments, it is expected that a display system wouldbe commonly implemented with a number of pixels of 1920×1080. In themeantime, a brighter light source such as a laser light source etc.starts to replace a high-pressure lamp to project illumination lightwith higher light intensities. With the implementation of the laserlight source, the size of a 1920×1080 micromirror array can be reducedfrom the current diagonal of about 0.95 inch to 0.7 inch or 0.5 inch.The size of the projection device can be further miniaturized.Furthermore, the gray scale levels for modern image display system arefurther increased from the current 8 bits to 10 bits and even to ahigher level of 16 bits.

However, with the above-mentioned developments and trends of themicromirror device used for image display, a micromirror is stilllimited by the restriction that the micromirrors are frequentlycontrolled to deflect for projecting the light according to a dualcontrol state as the ON light state or the OFF light state.

For example, when a micromirror device is used for a TV, a micromirrordeflects hundreds of billion times to satisfy a durability requirementthat the TV has a life time of at least five to ten years. Under thatrequirement, a micromirror is expected to touch and detach a micromirrorstopper hundreds of billion times. It is therefore necessary to considerthe improvement of the durability of the contact part between themicromirror and the stopper.

A mirror element typically implemented in a common micromirror devicehas a structure of supporting a micromirror formed by a reflection layerof aluminum, silver, etc. for reflection of incident light by an elastichinge formed by amorphous silicon, polysilicon, ceramics, aluminum, etc.on a substrate. Each micromirror further includes at least one addresselectrode on the substrate below the micromirror. The elastic hinge canbe a horizontal hinge of a twisted spring or a vertical hinge of a bentspring. Furthermore, the substrate is made of silicon, and an electriccircuit etc. connected to an address electrode is formed in thesubstrate. On the substrate or the address electrode, an insulatinglayer can be laid using the material of SiO₂, Al₂O₃, TiN, a-Si, etc. onthe substrate or the address electrode.

The micromirror device can be produced normally in a process similar toa semiconductor producing process. The manufacturing process mainlyincludes chemical vapor deposition (CVD), photolithography, etching,doping, chemical mechanical polishing (CMP), etc. Each mirror element ofthe micromirror device is controlled to deflect by a Coulomb force whena voltage is applied to the address electrode. The micromirror iscontrolled to deflect until it touches the insulating layer formed onthe stopper or the address electrode fixed on the substrate.

The problem of stiction between the micromirror and the stopper on thesubstrate or the contact part of the insulating layer may occur when themicromirror contacts the stopper of the electrode. The stiction occursdue to the surface tension generated by the water content in the aircondensed on the surface of the contact part on the substrate havingaffinity for water. Furthermore, the stiction can also occur due to theinter-molecule force, capillary force, electrostatic force, etc. betweenthe micromirror and the contact part on the substrate, etc. Theoccurrence of the stiction may cause a failure of control of amicromirror.

As a countermeasure to prevent the occurrences of the stiction,different configurations and methods are applied to reduce the surfaceenergy or decrease the area of the contact part. Alternately, theantistiction may be implemented by suppressing the friction of thecontacting surfaces between the micromirrors and the stopper orelectrodes.

In practical implementation, the micromirror modulator is also necessaryto enclose an inactive gas, for example, argon etc. in a package forprotecting a micromirror device and to guarantee the air-tightness orpreventing condensation due to a change of the temperature in theoperational environment. For these reasons, the antistictionconfigurations often become more difficult to implement.

Various countermeasures described below have been devised to prevent theabove-mentioned control failures due to the occurrences of stiction.

The U.S. Pat. No. 6,815,361 aims at preventing stiction by removing asacrifice layer during the production of a MEMS device. The patentedinvention discloses a method of piling an antistiction layer composed ofa polymer and polycrystal and processed by dry etching with aphotoresist. Then, a sacrifice layer is laid over the layer, and theantistiction layer and the sacrifice layer are simultaneously processed.The processes proceed by applying a wet etch to remove the sacrificelayer with an HF solvent and the antistiction layer is removed by dryetching.

The United states Patent Application Publication No. 2004/0136044discloses a technique of performing a surface stabilizing process orproviding a lube layer to reduce the stiction between a static part anda deflection part in a microstructure device having the deflection partconnected to the static part.

The U.S. Pat. No. 7,057,794 discloses a micromirror device having amultiplayer structure of mirrors. In the document, there is nodescription of stiction.

The U.S. Pat. No. 6,114,044 discloses the configuration of a film havinglow surface energy on the microstructure during the process based on aliquid. Specifically low surface energy film formed by a fluorinatedself-structured monolayer is provided on a microstructure device. Thus,a capillary effect generated between the components of themicrostructure device as a factor of stiction, and the viscosity betweenthe surfaces of microstructures close to each other are reduced.

The U.S. Pat. No. 5,602,671 and 5,411,769 disclose the technology offorming an oriented monolayer of a long-chain aliphatic halogenatedpolar compound including a carboxyl base (—COOH) such as PFDA(perfluorodecanoic acid; C₁₀HF₁₉O₂) having high durability with reducedsurface energy and friction coefficient to prevent the stiction causedby the force between molecules in the DMD. FIG. 3A shows a chemicalformula of the PFDA. FIG. 3B is a schematic diagram of the contact partat the tips of an electrode 38 and a mirror 36 after forming an orientedmonolayer of the PFDA.

The U.S. Pat. No. 5,576,878 discloses the technology of reducing thesurface energy and friction using separate metals having low affinityfor each other for two members contacting on a micromirror device toprevent stiction.

The United states Patent Application Publication No. 2004/0012061discloses the technology of using silicide precursor, for example, asiloxane material, silane, and silanol having a completely or partiallyfluorinated circular structure as an antistiction material forpreventing stiction.

The U.S. Pat. No. 5,447,600 discloses the technology of forming aprotective layer of fluorinated polymer such as Teflon-AF (amorphouspolymers) at a contact part of two members to prevent stiction on amicrostructure device.

The U.S. Pat. No. 5,579,151 discloses the technology of preventingstiction by laying an inorganic layer of a solid lubricant of SiC, AIN,or SiO₂ at a contact part between an electrode of a reflector and amirror in the spatial light modulation element including a reflectorcapable of being electrically charged and deflecting light. Especially,it discloses the technology of laying an inorganic surface stabilizer ona static member having a thickness of about 0.5 nm to 20 nm.

The U.S. Pat. No. 6,259,551 discloses the technology of forming amonolayer film of non-volatile molecules applied between monolayers at acontact part of two members of a microstructure device.

The U.S. Pat. No. 6,576,489 discloses the technology of coating byexposing a microstructure device to alkyl silane in a gaseous phase.

The U.S. Pat. No. 6,830,950 discloses the technology of preventingstiction by forming a hydrophobic self-structured monolayer using plasmaon the surface of a MEMS device. A precursor forming a self-structuredmonolayer can be, for example, OTS (octadecyltrichlorosilane;CH₃(CH₂)₁₇SiCl₃) or FDTS (perfluorodecyltrichlorosilane;CF₃(CF₂)₇(CH₂)₂SiCl₃). FIG. 4B shows the process of forming the FDTS ofthe self-structured monolayer on the surface of the MEMS device.

The U.S. Pat. No. 5,523,878 discloses the technology of covering thecontact part of the microstructure device with a monomolecule using theliquid phase growth of the self-structured monolayer or the precursor.It specifically discloses an example of covering the surface of thecontact part with the material of metal or aluminum oxide.

As described above, the technical difficulties of stiction are moreserious in a micromirror device implemented with large number ofmicromirrors. There is an urgent demand to resolve the difficulties suchthat the image display systems implemented with micromirror devicesovercome such technical problems to provide display images with improvedquality.

SUMMARY OF THE INVENTION

The first aspect of the present invention provides a micromirror deviceformed on a substrate supporting an elastic hinge for connection andsupporting a mirror on the substrate. The mirror device further includesan address electrode for receiving control signals for deflecting themirror, and a stopper for determining the maximum deflection angles ofthe mirror. A protective layer is formed on the substrate to cover atleast the stopper functioning also the address electrode providedbetween a portion below the mirror and the substrate, and an orientedmonolayer above the protective layer are laid.

The second aspect of the present invention provides a micromirror deviceformed on a substrate supporting an elastic hinge for connectionsupporting a mirror on the substrate. The mirror device further includesan address electrode for receiving signals for deflecting the mirror,and a stopper for determining the maximum deflection angles of themirror. A protective layer including a silicon material covers a stopperarranged closer with respect to a deflection axis of the mirror than thecenter of the address electrode on the substrate and the stopper, and anoriented monolayer is formed as the protective layer.

The third aspect of the present invention provides a micromirror deviceincluding an elastic hinge for connection and supporting a mirror on asubstrate, and a stopper for determining the maximum deflection anglesof the mirror. One side of the substantially square mirror is about 11μm or less, the gap between the mirror and an adjacent mirror is 0.55 μmor less, the distance between the lower bottom surface of the mirror andthe stopper is 1 μm or less, and an oriented monolayer having the numberof fluorinated carbon is 6 or less is deposited on the mirror, theelastic hinge, and the stopper.

The fourth aspect of the present invention provides a micromirror deviceincluding an elastic hinge composed of a silicon material for supportinga mirror on a substrate, an address electrode for deflecting the mirror,and a stopper for determining the maximum deflection angles of themirror. The stopper is provided between the portion below the mirror andthe substrate, and an oriented monolayer is deposited in the gap betweenthe elastic hinge and the stopper, or the gap between the mirror andalso deposited on the stopper that is equal to or smaller than the gapbetween the mirror and the address electrode, wherein the number ofcarbon fluorinated by the mirror, the elastic hinge, and the stopper is6 or less.

The fifth aspect of the present invention provides a micromirror deviceincluding an elastic hinge for supporting a mirror on a substrate, andan address electrode for deflecting the mirror. The address electrode isprovided on the substrate, a protective layer can be provided on theaddress electrode, and an oriented monolayer in which the number offluorinated carbon laid in a gaseous phase state is 6 or less isarranged in any of the mirror, the elastic hinge, and the protectivelayer.

The sixth aspect of the present invention provides a micromirror deviceincluding a stopper for determining the maximum deflection angles of amirror on a substrate. A protective layer made of an oxide to cover atleast the stopper is laid on the substrate, and an oriented monolayer islaid on the protective layer in a gaseous phase state under a normaltemperature and a reduced pressure.

The seventh aspect of the present invention provides a micromirrordevice including an elastic hinge for supporting a mirror on asubstrate, and an address electrode for deflecting the mirror. Theaddress electrode generates Coulomb force different from that of themirror depending on the direction of deflection of the mirror, aprotective layer can be laid on the address electrode, and at least anoriented monolayer laid on the address electrode in a gaseous phasestate is arranged.

The eighth aspect of the present invention provides a micromirror deviceincluding an elastic hinge for supporting a mirror on a substrate. Thedevice further includes at least a mirror array in which the gap betweena mirror and an adjacent mirror is 0.55 μm or less, a stopper fordetermining the maximum deflection angles of a plurality of mirrors, anelastic hinge which is enclosed by a plurality of stoppers and is widerthan the gap, and a stopper having an oriented monolayer laid throughthe gap.

The ninth aspect of the present invention provides the micromirrordevice according to the first through eighth aspects in which theoriented monolayer includes a halogenated alkyl silicide or an alkylsilicide.

The tenth aspect of the present invention provides the micromirrordevice according to the first through eighth aspects in which all or apart of hydrogen-H coupled to a carbon chain portion of the moleculehaving a carbon chain for forming an oriented monolayer is replaced withhalogen.

The eleventh aspect of the present invention provides the micromirrordevice according to the first through eighth aspects in which the carbonchain portion of the molecule having a carbon chain for forming anoriented monolayer makes saturated or unsaturated carbon coupling, andall or a part of hydrogen-H coupled to the carbon chain portion isreplaced with halogen.

The twelfth aspect of the present invention provides the micromirrordevice according to the first through eighth aspects in which theoriented monolayer includes a halogenated alkyl silicide or an alkylsilicide, and is made of two or more compounds having different numberof carbon or halogen.

The thirteenth aspect of the present invention provides the micromirrordevice according to the first through eighth aspects in which theoriented monolayer includes a halogenated alkyl silicide or an alkylsilicide, and is made of two or more compounds having different numberof at least carbon.

The fourteenth aspect of the present invention provides the micromirrordevice according to the first through eighth aspects in which theoriented monolayer is made of the material ofCF₃(CF₂)_(x)(CH₂)_(y)Si(CH₃)_(n)Cl_(3-n) (0≦n≦2).

The fifteenth aspect of the present invention provides the micromirrordevice according to the first through eighth aspect in which theoriented monolayer is configured by combining any one or two or more ofperfluorodecyltrichlorosilane, dichlorodimethylsilane, vinyl trimethoxysilane, octadecyltrichlorosinan, undecenyltrichlorosilane,decyltrichlorosilane, fluorooctatrichlorosilane,perfluorodecyldimethylchlorosilane, andperfluorooctyldimethylchlorosilane.

The sixteenth aspect of the present invention provides the micromirrordevice according to the first through eighth aspects in which the numberof the fluorinated carbon of the molecule configuring the orientedmonolayer is 6 or less.

The seventeenth aspect of the present invention provides the micromirrordevice according to the first through eighth aspects in which theelastic hinge includes a silicon material, and a material of one of As,P, Ge, and Ni is doped or spread.

The eighteenth aspect of the present invention provides the micromirrordevice according to the first through eighth aspects in which theprotective layer is SiC, amorphous silicon, or polysilicon.

The nineteenth aspect of the present invention provides the micromirrordevice according to the first through eighth aspects in which theprotective layer is SiC, amorphous silicon, or polysilicon, and furtherincludes a combination of oxygen and silicon, that is, —Si—O—.

The twentieth aspect of the present invention provides the micromirrordevice according to the first through eighth aspects in which theoriented monolayer is laid also on the side of the substrate.

The twenty-first aspect of the present invention provides themicromirror device according to the first through eighth aspects inwhich the oriented monolayer is configured by laying a plurality ofmonolayers.

The twenty-second aspect of the present invention provides themicromirror device according to the first through eighth aspects inwhich the oriented monolayer is configured by laying a plurality ofmonolayers, the end portion coupled to the substrate of the material ofthe first layer is halogenated silane, and the other end portion has anyof hydrogen, hydroxyl, and carboxyl.

The twenty-third aspect of the present invention provides themicromirror device according to the first through eighth aspects inwhich the oriented monolayer is configured by laying a plurality ofmonolayers, the first and second layers are made of different materials,the end portion of the material of the second layer coupled to theoriented monolayer film of the first layer is halogenated silane orcarboxyl, and the other end portion is —CF₃.

The twenty-fourth aspect of the present invention provides themicromirror device according to the first through eighth aspects inwhich the oriented monolayer is configured by laying a plurality ofmonolayers, the end portion of the oriented monolayer of the first layeris alkyl silicide, and the other end portion is hydrogen or halogenatedcarbon as hydroxyl.

The twenty-fifth aspect of the present invention provides themicromirror device according to the first through eighth aspects inwhich the oriented monolayer is configured by laying a plurality ofmonolayers, the first and second layers are configured by differentmaterials, the second layer is made of the material ofCF₃(CF₂)_(x)(CH₂)_(y)Si(CH₃)_(n)Cl₃ (0≦n≦2).

The twenty-sixth aspect of the present invention provides themicromirror device according to the first through eighth aspects inwhich the oriented monolayer is laid under a normal temperature and areduced pressure.

The twenty-seventh aspect of the present invention provides themicromirror device according to the first through eighth aspects inwhich the mirror line-contacts a point of the stopper or point-contactseach of at least two points of the stopper.

The twenty-eighth aspect of the present invention provides themicromirror device according to the first through eighth aspects inwhich Coulomb force is generated between the address electrode and themirror unit in the non-deflected direction while the mirror is deflectedin a predetermined direction.

The twenty-ninth aspect of the present invention provides themicromirror device according to the first through eighth aspects inwhich the Coulomb force between the mirror and the address electrode isreduced while the mirror is deflected in a predetermined direction.

The thirtieth aspect of the present invention provides a projectiondevice provided with a micromirror device including a mirror capable ofdeflecting and holding angles at which at least two optical state, thatis, an ON light state in which incident light is reflected toward aprojected light path and an OFF light state in which the incident lightis reflected in the direction other than the projected light path, adeformable elastic hinge for supporting the mirror arranged on thesubstrate, an address electrode for providing Coulomb force fordeflecting the mirror arranged on the substrate below the mirror, astopper regulating the deflection angle of the mirror, and a drivecircuit for providing a potential difference between the mirror formedon the substrate and the address electrode. With the configuration, thestopper includes a protective layer having Si, and one or two or morelayers of oriented monolayers including the molecules having the numberof halogenated carbon of 6 or less.

The thirty-first aspect of the present invention provides a projectiondevice provided with a micromirror device including a mirror capable ofdeflecting and holding angles at which at least two optical state, thatis, an ON light state in which incident light is reflected toward aprojected light path and an OFF light state in which the incident lightis reflected in the direction other than the projected light path, adeformable elastic hinge for supporting the mirror arranged on thesubstrate, an address electrode for providing Coulomb force fordeflecting the mirror arranged on the substrate below the mirror, astopper regulating the deflection angle of the mirror, and a drivecircuit for providing a potential difference between the mirror formedon the substrate and the address electrode. With the configuration, thegap between adjacent mirrors is 0.55 μm or less, the distance betweenthe lower bottom surface and the stopper is smaller than the length ofthe elastic hinge, and an oriented monolayer is laid on the addresselectrode or the stopper and the bottom surface of the mirror.

The thirty-second aspect of the present invention provides a projectiondevice provided with a micromirror device including a mirror capable ofdeflecting and holding an angle at which at least two optical state,that is, an ON light state in which incident light alternately emittedfrom a laser light source of a plurality of colors is reflected toward aprojected light path and an OFF light state in which the incident lightis reflected in the direction other than the projected light path, adeformable elastic hinge for supporting the mirror arranged on thesubstrate, an address electrode for providing Coulomb force fordeflecting the mirror arranged on the substrate below the mirror, and adrive circuit for providing a potential difference according to a videosignal of a given bit between the mirror and the address electrodeformed on the substrate. With the configuration, the incident light ofat least one color is emitted with pulses of a frequency of deflectionin the ON light state and the OFF light state higher than the frequencyof the number of given bits in one frame, and an oriented monolayer isprovided at a contact part in the deflection state of the mirror.

The thirty-third aspect of the present invention provides a projectiondevice provided with a micromirror device including a mirror capable ofdeflecting and holding angles at which at least two optical state, thatis, an ON light state in which incident light from a laser light sourceis reflected toward a projected light path and an OFF light state inwhich the incident light is reflected in the direction other than theprojected light path, a deformable elastic hinge for supporting themirror arranged on the substrate, an address electrode for providingCoulomb force for deflecting the mirror arranged on the substrate belowthe mirror, and a drive circuit for providing a potential differencebetween the mirror and the address electrode formed on the substrate.One side of the mirror is 10 μm or less, the deflection angle betweenthe ON light state and the OFF light state of the mirror is 20° or less,and an oriented monolayer is provided for a contact part in thedeflection state of the mirror.

The thirty-fourth aspect of the present invention provides theprojection device according to the thirtieth through thirty-thirdaspects in which the mirror continuously repeats free oscillationbetween the ON light state and the OFF light state, thereby maintainingthe free oscillation state in which the integration value of thequantity of light reflected toward the projected light path is madelower than the ON light, and preventing the mirror from contacting thestopper in at least one period in the free oscillation state.

The thirty-fifth aspect of the present invention provides the projectiondevice according to the thirtieth through thirty-third aspects in whichthe micromirror device is configured by a mirror array provided withabout two millions of pixels of substantially square mirrors, thesurface of the mirror has an aluminum or silver reflection surface, andthe thickness of the reflection surface is 2000 Å or less.

The thirty-sixth aspect of the present invention provides the projectiondevice according to the thirtieth through thirty-third aspects in whichthe effective length of the substantially perpendicular elastic hinge ofthe micromirror device is 1 μm or less.

The thirty-seventh aspect of the present invention provides theprojection device according to the thirtieth through thirty-thirdaspects in which the voltage for deflection control of the mirror or thevoltage for holding the mirror at the stopper is 15V or less.

The thirty-eighth aspect of the present invention provides theprojection device according to the thirtieth through thirty-thirdaspects in which the oriented monolayer is made of the material ofCF₃(CF₂)_(x)(CH₂)_(y)Si(CH₃)_(n)Cl_(3-n) (0≦n≦2).

The thirty-ninth aspect of the present invention provides the projectiondevice according to the thirtieth through thirty-third aspects in whichthe molecule configuring the oriented monolayer includes the number ofhalogenated carbon of 6 or less.

The fortieth aspect of the present invention provides the projectiondevice according to the thirtieth through thirty-third aspects in whichthe molecule configuring the oriented monolayer includes the number ofhalogenated carbon of 6 or less, and is laid under the normaltemperature and a reduced pressure in the gaseous phase state.

The forty-first aspect of the present invention provides the projectiondevice according to the thirtieth through thirty-second aspects in whichthe light source of the incident light is a semiconductor laser lightsource, and the F Number of the projection lens is 3.5 or more.

The forty-second aspect of the present invention provides the projectiondevice according to the thirtieth through thirty-second aspects in whichthe light source of the incident light is a semiconductor laser lightsource, the deflection angle between the substantially horizontal stateof the mirror and the ON light state or the substantially horizontalstate of the mirror and the OFF light state is 18° or less, and thedeflection angles of the ON light state and the OFF light state aresubstantially the same.

The forty-third aspect of the present invention provides the projectiondevice according to the thirtieth through thirty-second aspects in whichthe light source of the incident light is a semiconductor laser lightsource, the deflection angle between the substantially horizontal stateof the mirror and the ON light state or the substantially horizontalstate of the mirror and the OFF light state is 15° or less, and thedeflection angles of the ON light state and the OFF light state aredifferent from each other.

The forty-fourth aspect of the present invention provides the projectiondevice according to the thirtieth through thirty-third aspects in whichthe mirror has at least two states, that is, the ON light state and theOFF light state, the area or the position of the address electrode isdifferent between the ON light state and the OFF light state.

The forty-fifth aspect of the present invention provides the projectiondevice according to the thirtieth through thirty-third aspects in whichthe mirror has at least three states, that is, the ON light state, theOFF light state, and the oscillation state, and a voltage lower than thevoltage held at the stopper or 0V is applied in the oscillation state inthe ON light state or the OFF light state of the mirror.

The forty-sixth aspect of the present invention provides the projectiondevice according to the thirtieth through thirty-third aspects in whichthe deflection angles of the mirror from the horizontal state aredifferent between the ON light state and the OFF light state.

The forty-seventh aspect of the present invention provides theprojection device according to the thirtieth through thirty-thirdaspects in which the deflection angle of the mirror in the ON lightstate is 12° to 8° from the horizontal state of the mirror.

The forty-eighth aspect of the present invention provides the projectiondevice according to the thirtieth through thirty-third aspects in whichthe deflection angle of the mirror in the ON light state is 8° to 4°from the horizontal state of the mirror.

The forty-ninth aspect of the present invention provides the projectiondevice according to the thirtieth through thirty-third aspects in whichone of the Coulomb force for holding the mirror in the ON light stateand the Coulomb force for holding the mirror in the OFF light state islower than the other.

The fiftieth aspect of the present invention provides the projectiondevice according to the thirtieth through thirty-third aspects in whichone side of the mirror is 7 μm or less, and the gap from an adjacentmirror is 0.4μ or less.

The fifty-first aspect of the present invention provides the projectiondevice according to the thirtieth through thirty-third aspects in whichthe oriented monolayer is laid without heating the substrate or thechamber.

The fifty-second aspect of the present invention provides the projectiondevice according to the thirtieth through thirty-third aspects in whichthe elastic hinge is a torsion spring arranged substantiallyhorizontally to the mirror.

The fifty-third aspect of the present invention provides the projectiondevice according to the thirtieth through thirty-third aspects in whichthe elastic hinge is a bent spring arranged substantiallyperpendicularly to the mirror.

These and other aspects, objects and advantages of the present inventionwill no doubt become obvious to those of ordinary skill in the art afterhaving read the following detailed description of the preferredembodiment, which is illustrated in the various drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A includes a functional block diagram for showing a conventionalprojection display using a micromirror device;

FIG. 1B shows a top view of micromirror elements for illustrating thebasic principle of a micromirror device used for a projection display;

FIG. 1C is a circuit diagram that shows an example of the drivingcircuit of prior arts.

FIG. 1D is a timing diagram that shows the scheme of Binary Pulse WidthModulation (Binary PWM) of conventional digital micromirrors to generategrayscale;

FIG. 2 is a perspective view for showing the light incoming from thelight source to the micromirror device;

FIG. 3A shows a chemical formula of the PFDA (perfluorodecanoic acid;C₁₀HF₁₉O₂);

FIG. 3B is a schematic diagram for illustrating the configuration of thecontact part between the electrode and the tip of the mirror afterforming the oriented monolayer of the PFDA;

FIG. 4A shows chemical formulae of the OTS (octadecyltrichlorosilane;CH₃(CH₂)₁₇SiCl₃) and the FDTS (perfluorodecyltrichlorosilane;CF₃(CF₂)₇(CH₂)₂SiCl₃);

FIG. 4B is a schematic diagram for illustrating the processes of formingan FDTS of the self-structured monolayer on the surface of the MEMSdevice;

FIG. 5A is a top view of one mirror element shown in FIG. 2;

FIG. 5B is a side cross sectional view of one mirror element shown inFIG. 5A;

FIG. 5C is a schematic diagram for illustrating the processes of formingan oriented monolayer in each member through a gap between adjacentmirror elements;

FIG. 6A a side cross sectional view that shows one mirror element inwhich a micromirror including al oriented monolayer contacts an addresselectrode;

FIG. 6B a side cross sectional view that shows one mirror element inwhich an elastic hinge including an oriented monolayer contacts anaddress electrode;

FIG. 6C is a side cross sectional view that shows one mirror element inwhich an elastic hinge including an oriented monolayer contacts astopper formed on an address electrode;

FIG. 6D is a side cross sectional view that shows one mirror element inwhich an elastic hinge including an oriented monolayer contacts astopper;

FIG. 7A shows a chemical formula of the VTS (vinyltrichlorosilane;C₂H₃Cl₃Si) as a material of an antistiction layer;

FIG. 7B shows a chemical formula of the DDS (dichlorodimethylsilane;(CH₃)₂SiCl₂) as a material of an antistiction layer;

FIG. 7C shows a chemical formula of the PFODCS(perfluorooctyldimethylchlorosilane; CF₃(CF₂)₅CH₂)₂Si(CH₃)₂Cl) as amaterial of an antistiction layer;

FIG. 8A is a schematic diagram for showing the state of depositing thePFODCS (perfluorooctyldimethylchlorosilane; CF₃(CF₂)₅(CH₂)₂Si(CH₃)₂Cl)as a hydrophobic monomolecule on the surface of the substrate shown inFIG. 6A or 6B;

FIG. 8B is a schematic diagram for showing the state of depositing anoriented monolayer using two different hydrophobic monomolecules on thesubstrate surface as a variation example of FIG. 8A;

FIG. 8C is a schematic diagram for showing the state of depositing anoriented monolayer using a hydrophobic monomolecule obtained by couplingtwo different oriented monomolecules on the substrate surface as avariation example of FIG. 8A;

FIG. 9A shows the configuration of the drive circuit of one mirrorelement of a micromirror device in which an antistiction layer of anoriented monolayer;

FIG. 9B shows an alternate configuration of the drive circuit of amirror element shown in FIG. 9A;

FIG. 10A includes a side cross section view of a micromirror and atiming diagram to illustrate the operation at an ON state which reflectsincoming light fully for projection path;

FIG. 10B includes a side cross section view of a micromirror and atiming diagram to illustrate the operation at an OFF state which doesnot reflect incoming light for projection path;

FIG. 10C and a timing diagram to illustrate the operation a micromirrorand a timing diagram to illustrate the operation at an oscillating statewhich reflects incoming light for projection path partially; and

FIG. 11 is a functional block diagram for showing a system configurationand control schemes to implement digital and analog control signals inaccordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides a micromirror device implemented with anantistiction layer. The anti-stiction layer is to prevent stictionbetween the micromirror and the stopper on the substrate or themicromirror and the protective layer on the address electrode in eachmirror element.

In an exemplary embodiment, an oriented monolayer is laid on themicromirror device as an antistiction layer for preventing the stiction.A method of laying the oriented monolayer is carried out by forming avaporized oriented monolayer on each mirror array of a wafer followed bydicing the micromirror device in the chamber. The average movementenergy of a gaseous molecule having a mass m a can be represented by thefollowing equation (1) as the vaporized molecule undergoes a process atcertain temperature T.

$\begin{matrix}{{\frac{1}{2}{mv}^{2}} = {\frac{3}{2}{kT}}} & (1)\end{matrix}$Where m in the right side is a mass of the gaseous molecule, vrepresents an average speed of the gaseous molecule and k in the leftside represents a Boltzmann constant (k=1.38×10⁻²³ JK⁻¹), and Trepresents an absolute temperature.

Based equation (1), when the absolute temperature T is constant, theproduct of the mass m and the square of the average speed v of thegaseous molecule, that is, mv², is constant. According to equation (1),the average speed v of the gaseous molecule is obtained as follows.

$\begin{matrix}{v = {\sqrt{\frac{3{kT}}{m}} = \sqrt{\frac{3{RT}}{M}}}} & (2)\end{matrix}$

Where R represents a gas constant (R=8.31 Jmol⁻¹K⁻¹), and M representsthe molecular weight of the gas.

Therefore, a vaporized molecule moves at a higher speed with a higherabsolute temperature T¥. Under a constant absolute temperature, avaporized molecule with smaller mass M moves at a higher speed.Therefore, the speed of spreading a film on a surface is increased undert a constant absolute temperature T is increased with the film comprisesgaseous molecules of smaller molecular weight M. The time required tospread a film on a surface is therefore shortened when a film of smallermolecular weight is applied.

In exemplary embodiments of this invention, the molecular weights ofgaseous molecules applied for spreading a film on a surface may includemolecular weight of 482 g/mol for eprfluoroocrylrichlorosilane(CF₃(CF₂)₅(CH₂)₂SiCl₃; PFOTS), 384 g/mol forperfluoroocryldimethylchlorosilane (CF₃(CF₂)₂(CH₂)₂Si(CH₃)₂Cl; PFODSC),484 g/mol for perfluorodecyldimethylchlorosilane(CF₃(CF₂)₇(CH₂)₂Si(CH₃)₂Cl; PFDDCS), and 129 g/mol fordichlorodimethylsilane ((CH₃)₂SiCl₂; DDS).

When N gaseous molecules are contained in the box having the volume ofV, the average value of the distance of the moving gas per molecule,that is, a mean free path L, is expressed as follows.

$\begin{matrix}{L = \frac{V}{4\pi\; a^{2}N}} & (3)\end{matrix}$Where a represents a radius of one gaseous molecule.

Therefore, based on the equation (3), the mean free path L of thegaseous molecules depends on the molecule number density V/N and thesurface area 4πa² of the molecule. The smaller the radius of one gaseousmolecule, i.e., a, the longer is the mean free path L of the gas.Therefore, when a film is applied to spread on the surface of a devicemanufactured by MEMS technology with minute and complicated MEMSstructural features, it is advantageous to apply a gaseous molecule withsmall radius when different gaseous molecules have about the samedensity. Depending on the selected molecule, a film with improved filmintegrity is formed by heating the film and performing an annealingprocess in the process of spreading the film. Furthermore, a film can besuccessfully generated by laying a monolayer at a normal temperature orwith a reduced pressure at a normal temperature.

FIGS. 5A through 5C are schematic diagrams to illustrate the processesof applying the flow of the vaporized molecules to lay an orientedmonolayer. The oriented monolayer is applied to prevent stiction. Thestiction may occur on the reverse side of the reflection surface of amicromirror one of the mirror element of the micromirror device. Theoriented monolayer is to prevent the stiction between the lower surfaceof the micromirror and the surface of the stopper supported on thesubstrate.

FIG. 5A is a top view of a mirror element 23 arranged in atwo-dimensional array of the micromirror device as shown in FIG. 2. FIG.5A shows only one micromirror 21, an elastic hinge 53, and two addresselectrodes 52 a and 52 b as stopper portions. FIG. 5B is a side crosssectional view of FIG. 5A. FIG. 5B shows only the micromirror 21, theelastic hinge 53, two address electrodes 52 a and 52 b, and a substrate54. A vaporized molecule can have an oriented monolayer formed on eachof the address electrodes 52 a and 52 b, the elastic hinge 53, and thesurface of the reverse side of the reflecting surface of the mirror.FIG. 5C is a schematic diagram for illustrating the processes of formingan oriented monolayer for each member through a gap between micromirrors21 a and 21 b of adjacent mirror elements 23 a and 23 b in themicromirror device. In this example, control of deflection of themicromirrors 21 a and 21 b of the mirror elements 23 a and 23 b isperformed by address electrodes 57 a and 57 b. The address electrodesalso function as stoppers for limiting the tilt angle of the deflectablemirrors.

The vaporized mono-molecule forms an oriented monolayer on the surfacesof the address electrodes 57 a and 57 b, the elastic hinges 53 a and 53b, and the surface of the reverse side of the mirror reflecting surfacethrough the gap between the micromirrors 21 a and 21 b of each mirrorelement by a flow 56 of the gas shown in FIG. 5C.

Therefore, a gas flow that has a small gaseous molecule with a smallradius, i.e., radius a is selected. The molecules with small radius caneasily enter the gap between adjacent micromirrors, thereby more quicklyspreading an oriented monolayer on the surfaces of the stoppers and thesurface on the reverse side of the reflecting surface of themicromirror.

FIGS. 6A through 6D show the detailed layer structures of one mirrorelement provided with an antistiction layer formed according to theprocessing steps shown in FIGS. 5A and 5B.

The micromirror 21 that includes a plurality of mirror elements 23 shownin FIGS. 6A through 6D wherein the micromirror is substantially squarehaving a side of 4 μm through 14 μm. The micromirror 21 includes anupper layer functioning as a reflecting layer 66 (for example, analuminum layer) for efficiently reflecting light. The micromirrorfurther includes an intermediate layer of a support plate layer (forexample, a layer of titanium, tungsten, etc.) for supporting thealuminum layer, and a lower layer of a layer 65 formed with a silicon asthe same material for forming the elastic hinge 53.

The layer structure and materials implemented to form the micromirrorsmay have different optional selections. The mirror surface may becomposed of a bimetal layer obtained by laying an aluminum layer, asilicon layer, an aluminum layer, etc. in this order. The mirror surfacemay also a double layer structure of aluminum and silicon only. Thealuminum layer can basically reflect 80% or more of the visible lightwith the thickness of 1000 Å or less. In addition, the specific speed ofoscillation in the free oscillation state of the mirror can bedetermined as described later by adjusting the aluminum layer to a rangeof thickness between 1000 Å to 3000 Å to produce a predetermined weightof mirror.

The micromirror 21 of the mirror element 23 is arranged with a gap ofabout 0.09 μm through 0.55 μm from the adjacent micromirror 21. Thedimension of the mirrors and the gaps between the mirrors are controlledto prevent collisions with adjacent micromirrors when multiple mirrorsare control to simultaneously deflect and oscillate. The elastic hinge53 is coupled to a wiring layer (not shown) and extendingperpendicularly with respect to the substrate surface. The hinge 53 isformed on the substrate of a micromirror device, and is coupled to thelayer 65 composed of a silicon material that is the same as the bottomlayer of the micromirror.

The elastic hinge 53 is formed with a silicon material such as amorphoussilicon, polysilicon, monocrystal silicon, etc. The width of the elastichinge 53 is in a range between 0.5 μm to 1.2 μm, and the length isbetween 0.5 μm to 1.5 μm. The width and length of the hinge guaranteethe durability of the hinge to allow for the mirror to deflect andoscillate at a wide range of frequencies. Furthermore, instead of asingle hinge configuration, two narrow elastic hinges can be applied.The elastic hinge can be a torsion spring arranged substantiallyhorizontally to the micromirror 21.

In addition to the silicon material applied for forming the micromirror21 or the elastic hinge 53, additional materials may include arsenic,boron and phosphorus. By doping Si of the silicon material with arsenic,boron and phosphorus, the conductivity of the doped silicon thus allowsthe transmission of electrons from the micromirror 21 to the addresselectrodes 52 a and 52 b when a voltage is applied.

The Si may be doped by implanting arsenic, boron and phosphorus ionsinto the silicon substrate or by applying an in-site doping process. Inaddition to arsenic, boron and phosphorus, conductive materials such asgermanium, nickel, etc. can also spread on to the elastic hinge forproviding conductivity to the elastic hinge made of semiconductormaterial.

In the surface of the substrate around the area where the micromirrordevice is coupled to the elastic hinge 53, the drive circuit (not shown)is connected through a via to the address electrodes 52 a and 52 b forreceiving signals to control the deflection of the micromirror.

The substrate 54 shown as the bottom layer has a metal layer 62 coveredthereon. An oxide layer 63 covers over the metal layer 62. The addresselectrodes 52 a and 52 b and a stopper, etc. are formed on top of theoxidation layer 63. The address electrodes 52 a and 52 b may alsoimplemented to function as a stopper. The mirror is controlled byapplying voltages to the address electrodes 52 a and 52 b for generatingCoulomb forces between the address electrodes 52 a and 52 b and themicromirror 21 for controlling and deflecting and the micromirror 21different tilt angles.

Furthermore, a protective layer 64 formed with a silicon material as aninsulating layer covers over the surface of the address electrodes 52 aand 52 b. The protective layer 64 comes into contact with the layer 65on the bottom surface of the micromirror 21 when the micromirror isdeflected to one of the address electrodes. In an exemplary embodiment,the protective layer 64 is a layer composed of SiC or amorphous silicon,and polysilicon. By adding oxygen to the amorphous silicon orpolysilicon as the protective layer 64, a Si—O— coupling occurs, theelectric resistance value increases, and the insulation can be enhanced.

The distance between the address electrodes 52 a and 52 b and the lengthand height of the micromirror 21 are designed to allow for the mirror todeflect to specific deflection angle. The Coulomb force working betweenthe micromirror 21 and the address electrodes 52 a and 52 b can beadjusted by appropriately adjusting the distance between the addresselectrodes 52 a and 52 b and the micromirror 21, and the area of theaddress electrodes 52 a and 52 b. Application of the Coulomb force fordeforming the elastic hinge 53 that supports the micromirror 21 isnecessary to carry out the light modulation function of the micromirrordevice.

FIG. 6A shows an example of a mirror element in which the micromirror 21is control to tilt and contact the address electrodes 52 a and 52 bfunctioning as a stopper by applying a voltage to the address electrodes52 a and 52 b.

When address electrodes 52 a and 52 b functioning also as a stopperportion, the deflection angle of the micromirror 21 can be determinedbased on an angular position of the micromirror 21 where the micromirror21 touches the upper portions of the address electrodes 52 a and 52 b.

FIG. 6B shows an example of a mirror element in which the elastic hinge53 touches the address electrodes 52 a and 52 b by applying a voltage tothe address electrodes 52 a and 52 b. The deflection angle of themicromirror 21 is limited by the configuration of the elastic hinge 53that come into contact with the upper portions of the address electrodes52 a and 52 b.

FIG. 6C shows an example of a mirror element in which a projectionportion 68 of the address electrodes 52 a and 52 b is provided as astopper. With the configuration when the address electrodes 52 a and 52b are also implemented as the stoppers, the distance between the addresselectrodes 52 a and 52 b and the micromirror 21 can be shortened. Theshortened distance allows a control mechanism for controlling themicromirror with significantly increased Coulomb force. The shorteneddistance thus allows the application of a lower voltage to the addresselectrodes 52 a and 52 b.

FIG. 6D shows another exemplary embodiment of a mirror element in whicha stopper portion 69 is provided between the address electrodes 52 a and52 b and the elastic hinge 53. As shown in FIG. 6D, it is desired thatthe stopper portion 69 is arranged near the deflection axis of themicromirror 21, and the address electrodes 52 a and 52 b are arranged ata greater distance away from the deflection axis. With a greaterdistance between the mirror and electrodes, the Coulomb force betweenthe micromirror 21 and the address electrodes 52 a and 52 b is reduced.The arrangement of the position of the electrodes determines therotation moment according to the arrangement of the address electroderelative to the location of the deflection axis. In contrast, byarranging the stopper portion 69 closer to the deflection axis, theforce against the stiction force may be increased thus suppressing theproblems of stiction of the micromirror to the stoppers. If the stopperis configured to also function as an electrode, the Coulomb forcebetween a stopper and the micromirror also works in addition to theaddress electrodes 52 a and 52 b, thereby easily deflecting themicromirror 21

Although not shown in the attached drawings, a stopper structure havinga projecting part on the lower surface of the micromirror 21 can beprovided to adjust the micromirror 21 to have a different deflectionangle. The present invention discloses an antistiction layer 67 composedof an oriented monolayer covering each portion that includes a siliconmaterial exposed to an external field in a mirror element of amicromirror device. For example, in FIGS. 6A through 6D, theanti-stiction layer 67 covers the surface of the bottom layer 65 of themicromirror disposed on the reverse side of the reflecting surface ofthe micromirror 21, the side surface of the elastic hinge 53, thesurface of the address electrodes 52 a and 52 b and the protective layer64, etc. on the substrate.

An oriented monolayer can also be formed on the side of the substrate 54holding a two-dimensional mirror array of the micromirror device byspreading the oriented monolayer with each micromirror device diced froma wafer. Thus, anti-stiction protection can be provided against thesubmerge of the side of the substrate 54. Thus, by providing theantistiction layer 67 of an oriented monolayer, in FIGS. 6A through 6D,the inter-molecule force and the surface energy causing the stiction canbe reduced. The inter-molecular force and the surface energy can begenerate at the contact areas between the micromirror 21 and the addresselectrodes 52 a and 52 b, the contact part between the micromirror 21and the elastic hinge 53. The stiction can also occurs at the contactareas between the micromirror 21 and the stopper. By applying ananti-stiction layer, the force and energy that may cause the stictionare reduced, and the coefficient of friction can be decreased also,thereby preventing stiction.

FIGS. 7A through 7C show examples of the chemical formulae of somemolecules of the oriented monolayer as a material of the antistictionlayer 67. FIG. 7A shows the chemical formula of the VTS (vinyltrichlorosilane; CH₂═CHSiCl₃) as a material of the antistiction layer 67. FIG. 7Bshows the chemical formula of the DDS (dichlorodimethylsilane;(CH₃)₂SiCl₂) of the halogenated alkyl silane as a material of theantistiction layer 67. FIG. 7C shows the chemical formula of the PFODCS(perfluorodecyldimethylchlorosilane; CF₃(CF₂)₅(CH₂)₂Si(CH₃)₂(Cl) of thehalogenated alkyl silane as a material of the antistiction layer 67.Furthermore, a molecule of the oriented monolayer not shown in theattached drawings can be OTS (octadecyltrichlorosilan; CH₃(CH₂)₁₇SiCl₃),PFOTS (perfluorooctyltrichlorosilane; CF₃(CF₂)₅(CH₂)₂SiCl₃), UTS(undecenyltrichlorosilane; CH₃(CH₂)₁₀SiCl₃), DTS (decyltrichlorosilane;CH₃(CH₂)₁₁SiCl₃), and various other materials.

Thus, a molecule forming an oriented monolayer as a material of theantistiction layer 67 can mainly be halogenated alkyl silane and alkylsilane. When the molecule of the oriented monolayer as a material of theantistiction layer 67 has a carbon straight chain portion, all or a partof hydrogen-H coupled to the carbon of the carbon straight chain portioncan be replaced with halogen. Furthermore, a molecule of the orientedmonolayer having the carbon straight chain portion as a material of theantistiction layer 67 can be a carbon compound in which a carbon-carbonbond is saturated or unsaturated. In addition, a molecule of theoriented monolayer having a carbon straight chain portion in which acarbon-carbon bond is saturated or unsaturated as a material of theantistiction layer 67 can have all or a part of hydrogen-H coupled tocarbon replaced with halogen.

It is also preferable that a molecule of the oriented monolayer that has—CH₃ base, ═CF₂, or —CF₃ base at one end portion, and halogenated silaneor halogenated alkyl silane base at the other end portion is applied asa material of the antistiction layer 67.

The above-mentioned oriented mono-molecule reacts and is coupled withsilane in the member that includes Si to function as the protectivelayer 64 or the layer 65 that includes a silicon material as shown inFIG. 6A. The coupling is caused by the condensation reaction between theoriented mono-molecule having a halogen element at one molecule end andthe hydroxyl-OH on the substrate surface.

As a result, an unsaturated carbon bond or a long carbon chain isincluded in the oriented monolayer coupled to the substrate surface,thereby inducing the hydrophobic property on the substrate surface.Furthermore, the condensation reaction forms a non-conductive —Si—O—Si—coupling on the substrate surface, thereby increasing the resistancevalue and improving the electrical insulation. Furthermore,inter-molecule force can be reduced by placing ═CF₂ or —CF₃ outermost onthe substrate surface.

FIG. 8A shows the state of forming and spreading the PFODCS(perfluorodecyldimethylchlorosilane; CF₃(CF₂)₅(CH₂)₂Si(CH₃)₂Cl) as ahydrophobic monomolecule layer on the protective film of the micromirrordevice shown in FIGS. 6A through 6D. FIG. 8A is a diagram forillustrating the Cl of the halogen element at the end portion of thePFODCS reacts with hydroxyl-OH on the surface of the protective layer 64composed of the silicon material on the substrate surface, and thePFODCS forms —Si—O—Si— coupling with the protective layer 64.

In the process, Cl of the halogen element at the end portion of thePFODCS reacts with the hydroxyl-OH on the protective layer surface, andis removed as HCl. Thus, the PFODCS is —Si—O—Si-coupled on theprotective layer 64 of the substrate surface to form an orientedmonolayer.

In addition, since the bottom layer of the micromirror and the elastichinge are formed by a member including a silicon material having Si, allthe surface areas can be provided with a stable oriented monolayer byperforming a similar process.

FIG. 8B is a diagram to show the process of forming an orientedmonolayer using two or more different hydrophobic molecules on aprotective layer as a variation example of FIG. 8A. FIG. 8B shows as anexample of applying two different molecules, such as the OTS having onone end portion of one of the monomolecules a methyl-CH₃, and the FDTShaving —CF₃ of a high electric negative level, on the surface of theprotective layer 64 of the same substrate. In addition, the process mayalso use a DTS having on one end portion of a monomolecule a methyl-CH₃,the PFOTS having —CF₃ of a high electric negative level, etc. As in thecase shown in FIG. 8A, the OTS and the FDTS form —Si—O—Si— coupling onthe surface of the protective layer 64. Therefore, an oriented monolayerincluding two different compounds is formed on the surface of theprotective layer 64.

An oriented monolayer can also be formed on the surface of theprotective layer by using a mixture of two or more types of moleculeshaving different carbon numbers or halogen numbers of the orientedmonomolecules. In these processes, various hydrophobic states can beformed on the substrate surface depending on the specific processing andsurface conditions of a micromirror device. Thus, the antistiction layercan effectively prevent the stiction caused by the surface energy due tothe water content attached to the substrate at the contact part of twomembers of a micromirror device.

FIG. 8C shows the processing conditions of forming an oriented monolayerwith two or more different molecules are combined and coupled on theprotective layer of a substrate. For example, in FIG. 8C, the monolayeris processed by using a trichlorosilane-SiCl₃ of halogenated silane atthe end portion of one molecule coupled to the protective layer as amolecule of the first layer coupled to the protective layer, and theHPFHTS (hydroxy-perfluorohepthyltrichlorosilane; CF₂OH(CF₂)₄(CH₂)₂SiCl₃)having a hydroxyl-OH at the other end portion.

The HPFHTCS is applied to form the first layer to couple to a secondlayer. The FOTS having at one end portion a trichlorodilane-SiCl₃ of thehalogenated silane coupled to the hydroxyl-OH of the first layer, andhaving at the other end —CF₃ is coupled and applied as the second layer.The hydroxyl-OH can be replaced with carboxyl-COOH As shown in theexample, an oriented monolayer of a thick film identical to the moleculehaving the number of fluorinated carbon of 8 through 12 can be formed byusing an oriented monolayer. The monolayer is implemented with amolecule having a high film forming speed that has a low molecularweight of 6 or less of the number of fluorinated carbon coupled to twolayers. In the molecule coupled in the two layers, potentialenvironmental impacts can also be suppressed by decreasing the number offluorinated carbon. Plural molecules can also be coupled as plurallayers without limiting to two layers.

The descriptions below provide details of controlling a mirror elementformed with antistiction layer that includes an oriented monolayer.

FIG. 9A is a cross sectional view that shows the configuration of adrive circuit of one mirror element in a micromirror device providedwith an oriented monolayer. FIG. 9A shows a circuit that includes a FET(field effect transistor)-1 connected between the electrode 52 a, a bitline 1, and a word line. The circuit further includes a capacitanceCap-1 connected between the electrode 52 a and the GND. Similarly, aFET-2 is connected between the electrode 52 b, a bit line 2, and a wordline, and a capacitance Cap-2 is connected between the electrode 52 band the GND.

A drive circuit applies signals to the bit lines 1 and 2 and the wordline and also applying a predetermined voltage to the electrode 52 a tocontrol the mirror 21 to deflect toward the electrode 52 a.

Similarly, by controlling the signals of the bit lines 1 and 2 and theword line, a predetermined voltage may also be applied to the electrode52 b to tilt the mirror 21 toward the electrode 52 b. The drive circuitis formed and supported on the substrate of the micromirror device.

FIG. 9B shows an alternate embodiment of the drive circuit of the mirrorelement shown in FIG. 9A. In the this exemplary embodiment, one addresselectrode is implemented for controlling the micromirror 21 for onemirror element, and one address electrode 52 is arranged over the ONlight side and the OFF light side to which the micromirror 21 is held ina deflected state. In addition, one bit line and word line is providedfor a mirror element to transfer signal data to the address electrode 52for controlling of the deflection of one mirror element.

The micromirror 21 is controlled to deflect by one address electrode 52and one drive circuit. The deflection angle is designed and defined bythe area, the height, etc. of the address electrode 52 configured withasymmetric configuration relative to the elastic hinge and thedeflection axis of a mirror. A method for controlling the mirror tooperate from an initial state to move to the OFF state, and then deflectto the ON state. The control processes are dependent on the facts thatthe areas of the left and right address electrodes 52 are made differentin the elastic hinge 53, and the electrode having a larger area isplaced in the OFF state. The mirror is tilted to the address electrodethat has a larger area by applying a voltage to the address electrodefrom the initial state in which no voltage is applied.

It can be understood that there is a strong effect of the Coulomb forcebecause of a larger amount of electric charge are held in a larger areathan the ON state side where the address electrode has a smaller areathat the address electrode on the OFF state side. The effect of theamount of Coulomb force can be expressed by the Equation (4) below. Analternate embodiment may also be configured by setting an equal distancebetween the micromirror 21 and the address electrode 52 in the electrodeportion on the OFF side of the ON side electrode portion of the addresselectrode in the initial state.

$\begin{matrix}{F = {{\frac{1}{4\pi\; r^{2}} \cdot \frac{1}{ɛ}}q_{1}q_{2}}} & (4)\end{matrix}$where r represents the distance between the address electrode and themirror, ∈ represents a dielectric constant, and q₁ and q₂ represents theamounts of electrical charges. The control processes followed bycontrolling the micromirror 21 to tilt from the initial state to the OFFlight state and then enters a free oscillation state by temporarilysetting the voltage of the address electrode 57 to 0V. In the freeoscillation state, the micromirror can be placed at the ON side and heldin the ON state by applying a voltage at an appropriate time when themicromirror is close to an electrode that has a smaller area of theaddress electrode on the ON side.

With the Coulomb force F as defined by equation (4), the square of thedistance r has a more dominant factor than the amounts of charges q₁ andq₂. Therefore, when the areas of both ON side and OFF side of oneaddress electrode are appropriate adjusted, the Coulomb force F worksmore effectively on the micromirror that has shorter distance betweenthe address electrode and the micromirror even though the area of theelectrode portion on the ON side of the address electrode is smallerthan the electrode portion on the OFF side, thereby deflecting themicromirror toward the ON light side. As described above, themicromirror controlled by one address electrode and one set of wiring isdeflected from the initial state to the OFF light state, and then to theON light state.

Another method to control the deflection of a micromirror may also beimplemented by applying a voltage according to a multiple stageprocesses to the address electrode. For example, after keeping themirror to operate at a certain state by holding an ON state or an OFFstate with a voltage applied to an address electrode, the voltage of theaddress electrode is set to 0V, thereby set the micromirror in the freeoscillation state. Furthermore, the micromirror can be controlled in theON light state by applying a voltage weaker than the voltage used in theinitial state at an appropriately controlled time when the distancebetween the address electrode on the ON light side and the micromirroris still short while the freely oscillating micromirror is travelingfrom the ON side to the OFF side. Therefore, when the micromirror isfreely oscillating, and when the distance between the micromirror andthe address electrode is short, the micromirror can be controlled with alower voltage that is lower than the voltage applied when themicromirror is deflected from the initial static state to the ON stateor the OFF state.

Accordingly, the deflection of a micromirror can be controlled bysetting plural digital steps of voltage values for a mirror elementimplemented with one address electrode and one set of wiring. Byapplying a reduced voltage to control the micromirror also reduces theholding force of the micromirror to an electrode. The reduced holdingforce is advantageous in preventing the problem of stiction. FIGS. 10A,10B, and 10C are diagrams to show the control processes for deflecting amicromirror in the ON light state, the OFF light state, and theoscillation state. The mirror is deflected by applying a voltage to theaddress electrode in a mirror element implemented with an antistictionlayer of an oriented monolayer.

FIGS. 10A and 10B illustrate the changes of the reflection light whenthe micromirror is deflected to different angles. The ON position of amirror 21 is usually designated as the mirror position when the mirrorreflects the maximum brightness and the OFF position is designated for amirror position when the mirror reflects the minimum brightness withinthe drivable range of angles. By operating the mirrors 21 in thecondition for the mirror to reflect light partially, the micromirror maybe controlled to project incremental amounts of lights that is smallerthat the amount of lights represent by the LSB brightness. The controlmechanism thus allows to increase the total number of controllablegrayscales.

In the conventional systems, a mirror 21 is driven to an ON positionwith (0,1) signal applied to the electrodes 52 b beneath the mirror 21,wherein (0,1) is defined as zero volt is applied to the left electrode52 b and an ON voltage is applied to the right electrode 52 a asillustrated in FIG. 10A. In contrast, a mirror control signalrepresented by (1, 0) is applied to drive the mirror 21 to an OFFposition.

As illustrated in FIG. 10C, when a mirror 21 is controlled to operate inan oscillating condition, the light reflected from the oscillatingmirror as the output light is below that of ON position. Theoscillations of the mirror is controlled by providing two electrodes 52a,52 b under the mirror 21 with zero volts or (0, 0), when the mirror 21is in the position of ON or OFF state. A micromirror system implementedwith configuration shown in FIG. 1C according to the conventionaltechnologies cannot achieve such operations unless the system is changedto receive multiple bit input control.

Various computerized simulations revealed that the average reflectanceis from 20% to 40% depending on optical configurations. By choosing anoptical system suitably, the micromirror may be control to adjust thereflectance to 25% or ¼. This enables us to obtain ¼ of outputbrightness without changing the intensity of incoming light. By applyingmultiple pulses to the electrodes 52 a, 52 b under the mirror 21 asillustrated in FIG. 10C (the arrows in left side) in the middle of an ONposition, the amount of the reflecting light from the micromirror may becontrolled to achieve ¾ of reflectance. The voltages applied to theaddress electrodes 52 a and 52 b for holding the micromirror 21 may bereduced when the deflection angle of the micromirror 21 for the ON lightstate or the OFF light state is reduced. Conversely, when the deflectionangle of the micromirror 21 for the ON light state or the OFF lightstate is increased in order to recover the Coulomb force and the elastichinge 53 for holding the micromirror 21, the difference of the forcesapplied to the micromirror 21 for recovery can be freely set, and anadvantageous state can be appropriately set for reducing the probabilityof stiction. As described above, it is preferable to set lower force ofthe micromirror 21 in contacting the address electrodes 52 a and 52 bwhen also functioning as a stopper to prevent the problem of stiction.The contacting force can be reduced by reducing the potential differencebetween the address electrodes 52 a and 52 b and the micromirror 21 thusreducing the Coulomb force.

The following descriptions disclose the projection device that includesa micromirror device implemented with the above-mentioned orientedmonolayer. A projection device is configured such that the voltagesapplied to hold the micromirror at the deflection angles of the ON andOFF projection are non-symmetrical. An oriented monolayer is formed tocover the address electrode, the stopper, and areas below themicromirror. The reflection light along an ON direction is projected toa projection lens for projection of light for image display reflected bythe micromirror device.

Stiction of mirror may be prevented by increasing the frequency ofdeflecting the micromirror of the projection device toward OFF state orby increasing the time required for the micromirror to reach the OFFstate by reducing the potential difference between the address electrodeand the micromirror on the OFF light side.

Conversely, the stiction can also be prevented by reducing the potentialdifference between the address electrode and the micromirror on the ONlight side. However, a black pixel fault may occur. For this reason, animproved display quality may be implemented by reducing the potentialdifference in the OFF address electrodes instead of the ON addresselectrodes. Therefore, it is preferable to design the micromirror devicewith the electrode on the OFF light side despite the potential problemsof stiction.

Furthermore, the micromirror can be controlled to operate in the freeoscillation state, and the frequency of optical modulation control canbe set at a higher value to prevent the micromirror to have a prolongedcontact the stopper for preventing the occurrences of mirror stiction.With such control schemes, the projection gray scale levels can beincreased by precisely setting the quantity of light to be reflected andprojected by the micromirror.

In the free oscillation state in which a micromirror oscillates pluraltimes after temporarily contacting the stopper, it is further desirableto shorten the time of holding the micromirror onto the stopper. Thedurability requirement of an oriented monolayer on the surface of thestopper for the purpose of protecting against the stiction may also bereduced by implementing freely oscillating micromirror. More flexibilityis allow to select the antistiction material from a wide selection ofmaterials. According to the above descriptions, the stiction may beprevented by providing different control voltages during the freeoscillation operations in the ON light state and the OFF light state,and also by controlling the micromirror at a low voltage withoutstiction.

When the micromirror is in the horizontal state, the distance betweenthe micromirror and the address electrode is the longest, and therecovery force of the elastic hinge is at a lowest value. On the otherhand, when the micromirror contacts the address electrode or a stopper,the distance from the micromirror and the address electrode is theshortest, and the recovery force of the elastic hinge is at a highestvalue. The elastic hinge in this case has high recovery force inproportion to the amount of deformation of the elastic hinge. TheCoulomb force is generally inversely proportional to the square of thedistance between the address electrode and the micromirror. Therefore,the Coulomb force required to hold the micromirror for contacting theaddress electrode or a stopper is typically lower than the Coulomb forcerequired to drive the micromirror from the horizontal state.

Therefore, at the time when the micromirror contacts the addresselectrode or a stopper, the voltage applied to the address electrode isreduced. Thus, force holding the micromirror to the address electrode orthe stopper is reduced and the stiction can be further reduced.

In addition, at the time when the micromirror contacts either theaddress electrode or the stopper, the stiction can be further preventedby generating a Coulomb force in the direction of deviating from thecontact state of the mirror by applying a voltage to an addresselectrode arranged in the opposite direction.

Furthermore, the maximum deflection angle of the micromirror istypically in the range of 10° through 12° and is determined by theposition and size of the projection lens. Normally, when a brightnessprojection lens (for example, F number 1.8 etc.) is used, the diameterof the lens is large. Inversely, if a dark projection lens is used, aprojected image becomes dark. Taking the above-mentioned facts intoaccount, it is preferable to use a projection lens having an F-number ofabout 2.4. When the projection lens having the F number of about 2.4,the aperture NA is about 0.2, and it is preferable to configure aprojection system with the maximum deflection angle of about 12°.

The length of one side of a micromirror operated with only ON light orOFF light state is substantially between 10 μm through 14 μm.Accordingly, the length along the direction of the mirror deflection,i.e., along a diagonal direction of mirror, is between 14 μm to 20 μm.

Therefore, when the deflection angle is 12°, a maximum displacement ofabout 2 μm (=sin 12°×20 μm/2) at the tip of the micromirror isgenerated. Furthermore, when laser light is used as a light source, thedegradation of the spatial frequency at high resolution is lower thanwith a normal mercury lamp etc., thereby providing a sufficientresolution with a smaller diameter of the projection lens. In addition,since a laser is low in the spread of luminous flux and high instraightness, the brightness is not reduced even with a smallermicromirror device based. The advantage is achievable because of therelationship between the aperture NA and the etendue relating to theillumination area. Then, the size of the micromirror of the mirrorelement of a micromirror device further operated with the oscillationstate or the intermediate state can be designed for 14 μm through 4 μm.

With this configuration, when the maximum deflection angle of the mirrorin the oscillation state or the intermediate state is 6°, the tip of themicromirror is displaced by about 1 μm (=sin 6°×20μ/2), and the amountof displacement of the tip of the micromirror is about half the distancecompared with the micromirror operated with only the ON light or OFFlight states. When the deflection angle is 6°, NA=Sin 6°=0.1, the Fnumber of the projection lens is about 5, and an a small projection lenscan therefore be implemented.

By shortening the distance between the micromirror and the addresselectrode, the Coulomb force working between the micromirror and theaddress electrode is increased significantly because of the relationshipof inversely proportional to the square of the distance. It is furtheradvantageous that the address electrode is positioned in the deflectiondirection toward a smaller deflection angle of the micromirror. Suchconfiguration is designed in advance to set a short distance between themicromirror and the address electrode. The area of the address electrodecan also be increased to more effectively control the micromirrors. Withthe configuration, the voltage to be applied to the address electrodecan be controlled at a low voltage.

In an exemplary embodiment, when the micromirror size is 8 μm and thedeflection angle is 6°, the displacement at the tip of the micromirroris about 0.6 μm. Therefore, the minimum distance between the micromirrorand the stopper or the address electrodes can be 0.6 μm. As describedabove, in the micromirror device operable with an oscillation state orintermediate state may achieve a micromirror with reduced size.Furthermore, the control voltage for deflecting the micromirror into astopper can also be reduced. Furthermore, the gap between micromirrorscan also be reduced with smaller deflection angle. Because when themicromirror tilts, the distance of the displacement in the direction ofthe adjacent micromirror, along a horizontal direction, is alsoshortened.

When the micromirror has size of 8 μm and the gap is 0.35 μm, theaperture rate is about 90% or more. With a high aperture rate, thequantity of reflected light is increased, and a smoother image can beprovided without reducing the gap between the pixels of the projectedimages. Thus, it is important to select appropriate materials for layinga molecule as antistiction protection layer in producing a displaydevice of a small gap between mirrors and a short distance between themirror and the stopper.

In addition, when the micromirror size is reduced to 4 μm from theoriginal size of 7 μm, the total size of the micromirror device can alsobe miniaturized. When the micromirror size is 5 μm square, and thenumber of pixels is equivalent to XGA, the micromirror device can bereduced to about 0.25 inch in diagonal. With the number of pixelscorresponds to the HDTV, the micromirror device may be provided at asize of about 0.44 inch in diagonal. Thus, the micromirror device can befurther miniaturized. Therefore, using the small micromirror device, amore compact projection device can also be manufactured.

With the projection device using a plurality of smaller micromirrordevices, R (red), G (green), and B (blue) can be simultaneouslydisplayed. The problems of color break-up phenomenon can be prevented.Furthermore, with a projection lens to project the light reflected bythe micromirror device, the projection device implemented with aplurality of micromirror devices can present brighter images.

In the above-mentioned micromirror that has smaller size, the distancebetween a micromirror and an address electrode can be reduced, and thecontrol voltage for the micromirror or the voltage applied to theaddress electrode to hold the micromirror can be also be reduced. Thereduced voltage for holding the micromirror will further reduce theprobability of potential stiction problems.

Furthermore, the deflection angle of the micromirror can be differentbetween the ON light state and the OFF light state. It is preferable tomake the deflection angle for the OFF light state smaller. Alternately,it is preferable to make the distance between the address electrode andthe micromirror can be shorter for the OFF light side. The shorterdistance or smaller deflection angle reduce the necessary voltageapplied to the address electrode for deflecting the micromirror. Thus,the force for holding the micromirror to the address electrode and thestopper can be reduced, and therefore preventing the occurrences of themirror stiction.

According to current state of the art, the voltage for temporarilydeflection-controlling the micromirror from the horizontal state to theON light side and the OFF light side is performed by applying a voltageof about 20V. However, in the present embodiment, by operating themicromirror with reduced deflected angle, the micromirror is controlledby applying the voltage of about 5V to the address electrode. In thepresent embodiment, two-stage control voltages can be applied by firstapplying a voltage of 15V voltage and the subsequent application of avoltage of about 5V. The number of stages is not limited to two;multiple levels of control voltages may be flexibly applied. Therefore,the voltage for deflecting the micromirror can be reduced, the maximumcontrol voltage of the micromirror can be 5V through 15V, and theinitial control from the horizontal state of the mirror and themodulation control of the mirror can be conveniently carried out. Anexemplary embodiment, there is a transistor having the resistance toabout 12V according to the wiring rule of 0.18 μm, and the drive circuitfor controlling the micromirror can be simpler than in the prior art.

As described above, the present invention discloses the drive circuit ofthe micromirror controllable by a applying a lower voltage withoutincreasing the number of types of the control voltage.

In order to make a smaller micromirror and to project more smoothimages, it is necessary to reduce a gap between micromirrors from 0.55μm to 0.3 μm, 0.15 μm, and even 0.09 μm. The gap reduction is requiredbecause the quantity of reflected light of illumination light decreaseswhen the gap between micromirrors grows or a micromirror becomessmaller. Furthermore, the image quality of smoothness suffers withincreased gap between micromirrors as discontinuities between imagepixels are projected when there are larger gaps between themicromirrors. Therefore, when a micromirror device is used as a displaydevice of images, it is generally a design goal in making the smallestpossible gap between micromirrors for presenting a smooth image withimproved resolution by increasing the number of micromirrors withsmaller gaps.

Furthermore, a smaller gap between micromirrors, the required quantityof illumination light projected to an oriented monolayer from theirradiation of illumination light source can be decreased. Thedegradation of the oriented monolayer due to light irradiation can beprevented. Especially, since the light is projected with a high energyincluding an ultraviolet light area can degrade an oriented monolayer.It is therefore preferred to reduce the gaps between the micromirrorsthus reducing the intensity of illumination light thus protecting theantistiction layer from the light. In addition, laser light has recentlybeen widely used as an illumination light source. The light sourceprojecting brighter light of the illumination light is desired. Forexample, the brightness on the projection surface when white isdisplayed is to be preferably 500 nit or 800 nit or more. In this case,it is desired that a laser light source of about 2 w or 4 W be used fora reflective micromirror device. Such a laser light source includes asingle wavelength, and does not include a wavelength of the ultravioletlight area. Therefore, by using a laser light source of 2 W or more, thebrightness of the illumination light increases, but does not project alight with a wavelength of the ultraviolet light area. Such illuminationlight has less impact to cause the degradation of the oriented monolayerformed by an organic material. Thus, by using the laser light source of2 W through 4 W light output as an illumination light source, theillumination light for the projection device projected form the lightsource has brighter illumination than the conventional mercury lamp etc.The irradiation of the laser light on the micromirror device coveredwith a monolayer of an organic material is for antistiction can beoperated without degradation of an oriented monolayer, and a brightprojected image can be obtained.

This invention further discloses a configuration to reduce the thicknessof a micromirror less than the conventional thickness of about 3000 Å.With a reduced thickness, the recovery force or the potential differenceof an elastic hinge for deflecting a micromirror can be reduced, therebyreducing the occurrences of stiction.

Furthermore, this invention further disclosed a configuration forreducing the size of one micromirror to about 10 μm. Furthermore, themicromirror can be divided into two sub-mirrors. With the sub-mirrorconfiguration, the deflection from two sub-mirrors can be individuallycontrolled to further increase the gray scale levels. Thus, by dividingone micromirror into a plurality of sub-mirrors, the control voltage todrive one sub-mirror can be further reduced.

As described above, it is desirable to provide a projection deviceimplemented with a micromirror device that is configured as a mirrorarray of about 900 thousands or more pixels. The micromirror isconfigured in the form of substantially square mirror of 11 μm or less,the surface of a mirror has an aluminum or silver reflection surface,and the thickness of the reflection surface is 2000 Å or less.

In another exemplary embodiment, the micromirror device is configured asa mirror array of about 2 millions or more pixels in the form ofsubstantially square mirror of 8 μm or less, and the maximum deflectionangle of each micromirror is 14° through 4°.

In another exemplary embodiment, the micromirror device is controlled byapplying a different voltage to the address electrode to holdmicromirror at the ON state that that is applied to the OFF state. Inanother exemplary embodiment, the micromirror is controlled by a voltageof 15 volts of less for holding the micromirror at the stopper.

In another exemplary embodiment, the surface of the address electrode orthe stopper portion of the micromirror device is covered by SiC, Si, ora protective layer that includes Si. The protective layer of themicromirror device is formed by one or more of the materials of 6 orless halogenated carbon such as FOTS, PFODCS, etc. of an orientedmonolayer.

In another exemplary embodiment, the micromirror is formed by aplurality of layers. The bottom side of the reflection surface of themicromirror is configured by a layer including Si or a layer includingW, Ti, aluminum, etc. is the bottom side is provided with anantistiction layer formed by one or more of the materials of 6 or lesshalogenated carbon such as FOTS, PFODCS, etc. of an oriented monolayer.

In another exemplary embodiment, an antistiction layer is formed with anoriented monolayer covering the stopper and on the bottom surface of themicromirror device. The mirror gap of the mirror array of themicromirror device is 0.55 μm through 0.09 μm.

In another exemplary embodiment, the micromirror has at least two statesof the ON light state and the OFF light state, and the deflection angleof the mirror is different between the ON light state and the OFF lightstate. In another exemplary embodiment, the micromirror has differentareas of an address electrode or different positions of the addresselectrode between the ON light state and the OFF light state.

In another exemplary embodiment, the micromirror has at least threestates of the ON light state, the OFF light state, and the oscillationstate. In the oscillation state, the micromirror is controlled by avoltage lower than the voltage for holding it to the stopper portion inthe ON light state or the OFF light state.

Referring to FIG. 11 for describing an external signal received by themicromirror device for controlling the micromirror device. FIG. 11 is afunctional block diagram that illustrates an exemplary system of thisinvention. This system receives a 10-bit incoming signal. The ten-bitincoming signal is split into two parts, for example, upper 8 bits andlower 2 bits. The upper 8 bits are sent to the 1^(st) state controller,the lower 2 bits are sent to the 2^(nd) state controller and the syncsignal is sent to the timing controller. The 2^(nd) state controllerconverts the binary data to non-binary data.

Thus, the 1^(st) state and the 2^(nd) state can coexist and applied tocontrol the image display in one display frame. Furthermore, when thecontroller is applies the signal to control a single plate colorsequential system, each color of red, green, and blue is sequentiallydisplayed at 180 Hz or more. Preferably, the signals of three colors areprocesses and displayed at 360 Hz or more.

When a laser light source is used for as the light source of each color,a pulse emission is made according to the number of bits of a videosignal, and a micromirror is controlled to deflect and reflect the lightin each emission state.

For example, by applying an 8-bit video signal, the laser light sourceof each color is allowed to alternately emit a subframe once for an LSB(least significant bit) and twice for each other bit. A total of 15times (900 Hz) of alternate emission corresponding to each subframe isapplied to control the micromirrors. The micromirror is thereforecontrolled for deflecting the micromirror device corresponding to theemission period of the light source.

Furthermore, the control time of the 2^(nd) state may be assigned toeach of the sub-frames corresponding to the three colors of red, greenand blue. Additionally, the colors of cyan, magenta, and yellow may alsobe added to express images in 6 colors.

According to such control mechanism, the system increases the deflectingfrequency of the micromirror device in synchronization with the emissionfrom a light source in one frame. A shorter color switching period isachievable, and the color break-up phenomenon can be reduced, therebythe image display system presenting higher quality images, andincreasing the gray scale levels. In the system shown in FIG. 11, asignal splitter generates a sync signal. A timing controller controls aselector according to the sync signal, and allows the selector to switchcontrol of the micromirror device between the 1^(st) controller and the2^(nd) controller. Since the human visibility is highest on the color ofgreen, only green color is displayed in 14-bit gray scale, and othercolors are displayed in 12-bit gray scale.

According to this system configuration and control method, the frequencyof controlling the micromirror in the ON light state or the OFF lightstate increases. Furthermore, the illumination light of white includingred, green, and blue can be emitted separate from the colors of red,green, and blue. Furthermore, the, white can be displayed only in the1^(st) state. The descriptions of this patent application disclose themicromirror device for an image display system implemented withantistiction layer composed of oriented monolayer. Various advantagesand performance benefits are described in various exemplary embodiments.

The present invention has been described above with reference to someexamples of specific embodiments, but it is obvious that variations andamendments can be added to the embodiments within the scope of the gistof the present invention. Therefore, the specification and drawings ofthe present invention are not limited to any specific applications, butare regarded as examples only.

Although the present invention has been described in terms of thepresently preferred embodiment, it is to be understood that suchdisclosure is not to be interpreted as limiting. Various alternationsand modifications will no doubt become apparent to those skilled in theart after reading the above disclosure. Accordingly, it is intended thatthe appended claims be interpreted as covering all alternations andmodifications as fall within the true spirit and scope of the invention.

1. A micromirror device, comprising: an elastic hinge composed of aconductive material extends from a substrate for supporting a mirrorthereon; an address electrode for receiving an electrical signal todeflect the mirror; a protective layer covers and insulates the addresselectrode; and an oriented monolayer composed of a compound of aplurality of oriented mono-molecules covers the back surface of themirror, and the protective layer as an anti-stiction layer.
 2. Thedevice according to claim 1, wherein: the oriented monolayer is composedoriented mono-molecules of a halogenated alkyl silicide or an alkylsilicide.
 3. The device according to claim 1, wherein: the orientedmonolayer is composed of a compound of two or more orientedmonomolecules of coupled molecules of different number of at leastcarbon or halogen.
 4. The device according to claim 1, wherein: theoriented monolayer is composed of a combination of one or two or more ofa group of oriented mono-molecules consist ofperfluorodecyltrichlorosilane, dichlorodimethylsilane, vinyl trimethoxysilane, octadecyltrichlorosinan, undecenyltrichlorosilane,decyltrichlorosilane, fluorooctatrichlorosilane,perfluorodecyldimethylchlorosilane, andperfluorooctyldimethylchlorosilane.
 5. The device according to claim 1,wherein: the oriented monolayer is composed of a plurality of monolayerseach comprises plurality of oriented mono-molecules.
 6. The deviceaccording to claim 1, wherein: the oriented monolayer is composed of aplurality of monolayers each comprises plurality of orientedmono-molecules wherein an end portion coupled to the substrate of afirst layer is halogenated silane, and an opposite end portion of thefirst layer comprising of hydrogen, hydroxyl, or carboxyl.
 7. The deviceaccording to claim 1, wherein: the oriented monolayer is composed of aplurality of monolayers; a first and second layers are composed ofdifferent materials; and an end portion of the material of the secondlayer coupled to the oriented monolayer film of the first layer ishalogenated silane or carboxyl, and an opposite end portion is —CF₃. 8.The device according to claim 1, wherein: the oriented monolayer iscomposed of a plurality of monolayers each comprises plurality oforiented mono-molecules; and an end portion of a first orientedmonolayer is alkyl silicide, and an opposite end portion is hydrogen orhalogenated carbon as hydroxyl.
 9. The device according to claim 1,wherein: the oriented monolayer is composed of a plurality of monolayerseach comprises plurality of oriented mono-molecules; and a first and asecond layers are composed of different materials; and the second layeris composed of CF₃(CF₂)_(x)(CH₂)_(y)Si(CH₃)_(n)Cl_(3-n)(0≦n≦2).
 10. Thedevice according to claim 1, comprising: a mirror array comprises aplurality of mirrors each having substantially a square shape having awidth about 11 μm or less, and a gap of 0.55 μm or less between twoadjacent mirrors.
 11. The device according to claim 1, wherein: adistance between a lower surface of the mirror and a top surface of theprotective layer is 1 μm or less.
 12. A method for producing amicromirror device, comprising: forming a plurality of elastic hingesextended from a substrate wherein each of said hinges supports a mirrorthereon with two of adjacent mirrors having a gap of approximately 0.55μm or less and wherein said hinge is composed of a conductive materialhaving a width greater than the gap between two of said adjacentmirrors; forming a stopper on a top surface of said substrate adjacentto the hinge for stopping the mirror at a maximum deflection angle;forming an address electrode to receive a signal for deflecting themirror; and forming a protective layer to cover and insulate the addresselectrode; and forming an oriented monolayer composed of a compound of aplurality of oriented mono-molecules to cover the bottom surface of themirror, the stopper, and the protective layer as an anti-stiction layerfor preventing a stiction between the bottom surface of the mirror, thestopper and the address electrode.
 13. A projection device comprising: amicromirror device comprising: a mirror supported on a deformable hingeextended from a substrate for deflecting to different angles forreflecting an incident light to an ON light state and an OFF lightstate; an address electrode disposed on a top surface of the substratebelow the mirror to receive mirror control signals for generating aCoulomb force for deflecting the mirror to said different angles; astopper disposed near the hinge for stopping the mirror at a maximumdeflection angle; and a drive circuit for generating and transmittingthe mirror control signals to the address electrode, wherein the stopperis covered by two or more different types of oriented mono-layerscomposed of a compound with molecules containing six halogenated carbonor less.